ONE-DIMENSIONAL BIMODAL MODEL OF VIBRATION AND IMPACTING OF INSTRUMENT TUBES IN A BOILING WATER-REACTOR

The vibration and impacting of an instrument tube in a boiling water r eactor (B WR) have been studied using a one-dimensional bimodal model. Four modal nonlinear boundary conditions have been applied, and a set of coupled nonlinear equations describing the temporal evolution of t wo continuous modal amplitudes have been obtained. These equations hav e been numerically solved by means of a generalized Runge-Kutta algori thm for stochastic equations. The theoretical results have been compar ed with experimental in-core neutron noise measurements performed in a 1300-MW BWR, Gundremmingen C, and have been used to interpret the par ticular vibration behavior of one instrument tube.